Multiple plate tip or sample scanning reconfigurable scanned probe microscope with transparent interfacing of far-field optical microscopes

ABSTRACT

The invention is directed to a scanned probe microscope including one plate allowing for tip scanning and the other allowing for sample scanning, with the optical axis of the scanned probe microscope being free to permit incorporation into standard optical microscopes. The top plate can be hinged onto the bottom plate, or the top plate can simply be placed on the bottom plate and a rough approach is caused by a dc motor or other mechanism which will enable the two flat plate scanners to have a large z range. In another embodiment, the microscope includes three plates which allow sample scanning, tip scanning and two tips to be operational at the same time.  
     A microscope in accordance with the invention may use a liquid cell, may use a near-field optical element made of silicon cantilever technology, or may use an apertureless probe for apertureless near-field scanning optical microscopy.  
     The microscope may use a tuning fork for feedback in any combination of geometries of tip, sample and tuning fork and with or without gluing of the tip to the tuning fork and with control of tip attachment or near-attachment to the tuning fork. The control of tip attachment to the tuning fork may be based on near zero backlash movement technology, and the tuning fork can be used in non-contact, contact and intermittent contact modes of operation. A fiber based feedback system may use either straight or cantilevered fibers, and the detection of signals may be based on amplitude, phase, wavelength or other optical parameters that can be used to monitor the movement of an SPM sensor.

FIELD OF THE INVENTION

[0001] The field of this invention is the design of a unique ultra-thin scanning probe microscope that can readily operate and be flexibly re-configured in various different modes of operation with features that have never been previously available. The invention permits unique capabilities in scanned probe microscopy while allowing for full integration with a far-field optical microscope upright or inverted. It also allows for ready integration into low temperature optical cryostats and for use with various accessories. It also allows a variety of tip scanning schemes to be implemented.

BACKGROUND OF THE INVENTION

[0002] Scanned probe microscopes (SPM) have passed through many phases of development in the past two decades. A critical juncture in the development of these microscopes was the application of the tube piezoelectric scanner, which had previously been used for many years in the phonograph. This scanner was used first in atomic force microscopes (AFM) [G. Binnig and D. P. E. Smith, Rev. Sci. Instrum. 57, 1688 (1986)], which has led the way in the development of a whole variety of similar microscopes that are generally classed as SPMs.

[0003] In addition to the above, a SPM design was developed which used three tube scanners, which could scan a sample by coordinated operation [K. Besoka, Surf. Sci. 181,145 (1986)]. Furthermore, a four tube scanner was also described which allowed sample scanning by coordinated operation of the piezoelectric elements [K. Lieberman, N. Ben-Ami and A. Lewis, Rev. Sci. Instr. 67, 3567 (1996)].

[0004] Finally, a feedback mechanism was patented based on tuning forks used in watches [K. Karrai and M. Haines, U.S. Pat. No. 5,641,896] for scanning the probe or the tip that is used in SPM in close proximity to the sample. The tuning fork acts to control distance and to provide a method of distance regulation for a tip relative to the sample. This patent, however, was limited in that it required a specific direction of motion of a straight tip relative to the straight tip axis and the sample, and allowed only the use of shear force rather than normal force feedback.

[0005] The Karrai and Haines mechanism was invented for, and has been used extensively in, near-field scanning optical microscopy (NSOM). In these scanned probe microscopes an optical fiber is pulled to a small conical tip and this conical tip is coated with metal to form an aperture. Light is then passed through the optical fiber and emanates from the aperture with the dimension of the aperture.

[0006] The conical tip could be attached to one of the tines of a tuning fork for distance regulation of the tip and the sample. In this method the tuning fork resonates at a specific resonant frequency, which is generally used as a reference in watches. A straight fiber ending in a conical tip as described above is attached along one of the tines of the fork in a very specific geometry with the tip extending from the tine. The rest of the fiber is placed along the length of the tuning fork and is attached on the entire length. On this assembly a frequency is imposed. As the tip/tuning fork assembly approaches a surface with the tip oscillating at the imposed frequency there is an alteration in the tuning fork oscillation amplitude and phase and this is used to alter the position of the tip so that a tip/sample distance is maintained.

[0007] As noted above, the invention of Karrai and Hines was very limiting since it could be used only in a a specific geometry of tuning fork/straight optical fiber assembly. However, of even more importance is that it became evident, during the use of such assemblies, that the characteristics of the tuning fork could be drastically affected by attaching an optical fiber tip to one of its tines, and this was independent of other geometries that were attempted [[H. Muramatsu, N. Yamamoto, T. Umemoto, K. Homma, N. Chiba and M. Fujihara, Jpn. J. Appl. Phys. 36, 5753 (1997)] and silicon cantilevers on one of the tines of a tuning fork [W. H. J. Rensen, N. F. van Hulst, A. G. T. Ruiter and P. E. West, Appl. Phys. Lett. 75, 1640 (1999)].

[0008] One alteration, that was specifically important, was the reduction in Q factor in an uncontrolled fashion. Recently [D. N. Davydov, K. B. Shelimov, T. L. Haslett and M. Moskovits, Appl. Phys. Lett. 75, 1796 (1999)], there was an attempt to address this problem. These workers suggested that one of the reasons for this alteration in Q factor was a breaking of the symmetry of the tuning fork when such a fiber tip was attached to one of the tines [D. N. Davydov, K. B. Shelimov, T. L. Haslett and M. Moskovits, Appl. Phys. Lett. 75, 1796 (1999)]. These workers indicated that the placement of the straight optical fiber tip in a position that minimized the symmetry breaking could affect the extent of alteration of the Q factor. In addition, the mass of the fiber was given as another reason for the problems with tuning fork techniques. However, no direct control on the extent of the alteration in the Q factor was achieved. The problems raised by Davydov et al are symptomatic of the general problems of the tuning fork technique.

[0009] Tube scanning systems either with or without tuning forks have previously been employed to design either microscopes for sample scanning or to design microscopes for tip scanning, but in all the years since the introduction of the tube scanner or the tuning fork for straight tip shear force feedback, it has not been possible to design a microscope that had both tip and sample scanning.

[0010] Furthermore, a method and a device for controlled loading of a tuning fork/tip assembly has not been described in the prior art, and the geometries for tip and tuning fork that this control permits, in the present invention, could not be achieved. In addition, no method previously existed to lower, in a controlled fashion, the mass of the glue required for attaching a scanned probe tip to a tuning fork, which our invention indicates is a major problem in using such a method of feedback and in achieving usable geometries in order to form a tip/sample scanning scanned probe microscope. In addition, there is no report of a tuning fork system that has been designed without the need for gluing the tip to the tuning fork. Finally, the variety of other methods of tip feedback available in accordance with the present invention and that permit the tip/sample scanning microscope system of the invention, have not previously been described.

[0011] In addition, no prior tip scanning microscope could be placed on an upright conventional optical microscope so that the lens of the upright microscope could simultaneously view the scanned probe microscope during operation. This is important, not only to position the tip in the wider field of view but also to simultaneously collect light from a sample illuminated with a tip suitable for near-field scanning optical microscopy. It is also crucial for calibration of the optical microscope image with the near-field optical and atomic force microscopy tip.

[0012] All of the above is true not only for commercial versions of SPMs but for any reported laboratory versions.

SUMMARY OF THE INVENTION

[0013] In accordance with the present invention, it has been discovered that neither the symmetry of the placement of the tip on the tuning fork nor the mass of the fiber are the important elements in producing the less than ideal characteristics of tuning forks; instead, the present invention indicates that the main problem is the glue that is used to attach the fiber to the tuning fork. Accordingly, the invention is directed to an approach that allows for the loading of a tuning fork in a way that resolves the foregoing problems in a reproducible way. The invention is also directed to a variety of other methods for feedback that compete with tuning fork feedback even when tuning fork feedback is working optimally as a result of the present invention.

[0014] The present invention develops one of three different methods for scanning cantilevered silicon or glass AFM type tips in order to use flat scanners to develop a unique scanning probe instrument that is based on a series of interchangeable ultra-thin plates that allow tip and sample scanning in a variety of emulations.

[0015] As part of this development, a method and a device for controlled tuning fork/tip assembly are provided to achieve the geometries for tip and tuning fork that permit a tip/sample scanning SPM to be built. In addition, the invention describes a method to lower, in a controlled fashion, the mass of the glue remaining after attaching a scanned probe tip to a tuning fork or to completely eliminate the glue in this assembly. This method is applicable not only to the present tip/sample scanning design but to all uses of tuning forks. Furthermore, it has been found that the loading of the tip on the tuning fork must be accomplished without inducing axial deformation and extension in the fiber, and this is also applicable not only to the present tip/sample scanning design but to all uses of tuning forks. Finally, other approaches to feedback are described that allow for the improved tip/sample scanning design of the invention.

[0016] The ultra-thin SPM microscope that results from the present invention incorporates the first tip scanning system that can be placed on any optical microscope upright or inverted. It is the first SPM that permits tip or sample scanning in the same instrument and that can be switched from an AFM mode of operation where the tip is in non-contact or intermittent contact with the sample to a contact mode of operation where the tip is in contact all the time with the sample. It is also the first tip or sample scanning system that permits all the lenses of an upright optical microscope to be rotated freely during SPM operation, and is the first SPM that permits two independently controlled tips to be brought in contact with a sample. The invention readily allows the microscope to be inserted into an optical or other cryostat for low temperature operation with one or all of the features noted above. It can also be used for confocal optical microscopy and can work with accessories that permit operation in a liquid environment.

[0017] Accordingly, the invention is directed to a two plate scanned probe microscope including a top plate and a bottom plate, one plate allowing for tip scanning and the other allowing for sample scanning, with the optical axis of the scanned probe microscope being free to permit incorporation into standard optical microscopes. In one embodiment of the invention, the top plate can be hinged onto the bottom plate and a rough approach of the probe to the sample is caused by a dc or other motor. In another embodiment, the top plate is simply placed on the bottom plate and a rough approach is caused by a dc motor or other mechanism which will enable the two flat plate scanners to have a large z range.

[0018] In another embodiment, the top plate is replaced with one having regular beam deflection while keeping the optical axis free, and in still another embodiment, the microscope includes three plates which allow sample scanning, tip scanning and two tips to be operational at the same time. A flat plate tip scanner can work with any chosen scanning stage including those that are attached to regular microscopes.

[0019] The device of the present invention works within the confines of a conventional cryostat in which the sample can be cooled to as much as 4° K.

[0020] A microscope in accordance with the invention may use a liquid cell in which a sample is held in a sample scanning plate and a tip is held in a tip mount in the tip scanner plate and may include a top plate that works using standard beam deflection technology but with the optical axis of the device unobstructed for viewing with a lens. This lens may be a solid immersion lens. The microscope may also use a near-field optical element made of silicon cantilever technology, and may use an apertureless probe for apertureless near-field scanning optical microscopy. The microscope may also be used for atomatic and semi-automatic assembly of optical components, including fibers and fiber lenses with added lasers and other devices, and including welding or other procedures for attachment of components or other devices, may be used.

[0021] The microscope may use a tuning fork for feedback in any combination of geometries of tip, sample and tuning fork and with or without gluing of the tip to the tuning fork and with control of tip attachment or near-attachment to the tuning fork. The control of tip attachment to the tuning fork may be based on near zero backlash movement technology, and the tuning fork can be used in non-contact, contact and intermittent contact modes of operation. A fiber based feedback system, with single or multiple channel fibers for beam delivery and collection for feedback, may use either straight or cantilevered fibers, and the detection of signals may be based on amplitude, phase, wavelength or other optical parameters that can be used to monitor the movement of an SPM sensor. The feedback signal may be based on internally reflected light from a subwavelength tip at the tip of a waveguide, if desired.

[0022] The invention is also directed to a method of scanned probe microcopy which uses a two plate scanned probe microscope, one allowing for tip scanning and the other allowing for sample scanning, with the optical axis of the scanned probe microscope being free for incorporation into standard optical microscopes, wherein a tuning fork is used for feedback in any combination of geometries of tip, sample and tuning fork and with or without gluing of the tip to the tuning fork and with control of tip attachment or near-attachment to the tuning fork. The control of tip attachment to the tuning fork is based on near zero backlash movement technology, and the tuning fork can be used in non-contact, contact and intermittent contact modes of operation. A fiber based feedback system with single or multiple channel fibers for beam delivery and collection for feedback with these fibers being either straight or cantilevered and detection of signals

[0023] Finally, all of the above methods can be used in a variety of contact, intermittent contact or non-contact modes of AFM operation and any other such emulations of tip/sample scanning systems. In addition, although certain geometries and materials are employed in much of the discussion above, a variety of emulations are possible with different materials such as bimorphs, other piezo ceramic materials including those that have piezoresistive coatings, and different geometries for the imaging sensor and the feedback sensor etc. Also, in the case of a multichannel fiber, a laser can be delivered through one of the channels for transient heating and cooling of the cantilever for gentle cantilever oscillation without piezoelectric elements and in a way that provides very high resolution.

[0024] An example of a tip/sample scanning multiple plate reconfigurable microscope in accordance with the present invention, not to exclude other emulations, is a two plate version illustrated in FIG. 12 at (12.1) and (12.2), with two of the plates allowing for either tip or sample scanning. In this mode of operation, the two plate tip/sample scanning microscope can be inserted between the lens (12.3) and the sample stage (12.4) of a standard upright optical microscope with all the lenses of the microscope freely rotatable. The long range motion of the plates can be simply due to the large range of such flat scanning plates or, as shown, a device such as a stepping motor (12.5), inchworm, any dc motor etc. can be used for the far approach of the tip to the sample (12.6). The tip scanning plate can then be lifted off or detached if it is either screwed on, or clipped on or attached by some other means to the bottom plate and a plate for conventional contact operation (13.1) can be inserted (see FIG. 13) with a diode laser (13.2) and position sensitive detector (PSD) (13.3).

[0025] Alternately, the same tip scanning upper plate (12.1) can be used, with a diode laser and a position detector added onto this plate. With the tip and sample scanning plates in place, the instrument allows for a z extension between the sample and the tip of as much as 0.2 mm without the use of stepping motors, inchworms and the like. This has never been possible previously. With one of the plates in place this extension will be reduced to half the 0.2 mm value.

[0026] Many accessories, including liquid cells, can be used with these unique new microscopes. In one emulation, with the top plate as in FIG. 13, the liquid cell would have the following structure for appropriate beam deflection. Liquid cell operation is also feasible with other methods of beam deflection described above such as with tuning fork-like feedback. Small emendations would then have to be made in the design of the liquid cell seen in FIG. 14.

[0027] In the design in FIG. 14, the tip mount (14.1) is placed on a top plate that can either be a scanning plate or a non-scanning plate, and the liquid cell (14.2) is placed on the sample bottom plate of the microscopes described above. In addition, there are two channels (14.3) for the entrance and exit of liquid in order to exchange the liquid in the liquid cell.

[0028] The construction of the tip mount as illustrated in FIG. 15 includes a glass window glued to the bottom of the conical bore (15.1) in the tip holder. Also illustrated are two ferromagnetic poles (15.2) and (14.4) of a magnet. These poles form a magnetic circuit with an air gap or window, and between these two poles sits the tip holder that contains the tip. Above this region sits a magnet (14.5) that imposes a magnetic field. The tip holder is positioned so that the tip sits below the window (15.3).

[0029] As illustrated in FIG. 16, when a liquid cell is used with the conventional beam deflection system for feedback, a double bridge design is placed above the window to direct the light to the tip (16.1) and after that to direct the reflected light to the photodetector (16.2). This bridges consists of two mirrors with a gap, and because of the gap between these two mirrors this maintains the view of the sample with an upright microscope from the top. The design gives flexibility to adjust both bridges in terms of the spacing between the two mirrors and also in terms of the relative angle.

[0030] In another possible arrangement, this multiple plate SPM instrument can be built with the capability to scan independently two tips in addition to allowing sample scanning. This is another capability that no previous SPM instrument has ever had. To accomplish this, three plates placed one on top of another are used, as illustrated in FIG. 17. The two outer plates (17.1) and (17.2), respectively, can scan the sample or the tip while a plate (17.3) sandwiched between these two plates can also hold a tip. The tip on this plate, in one emulation, is brought in contact with the sample using piezoelectric tip modulation and the electrically or optically based detection methods described above.

[0031] Feedback can be accomplished with the sample scanning plate, or the intermediate plate holding this tip could have the same feedback and scanning capabilities as plate (17.2). The tip scanning outer plate (17.2) will hold the second tip. This tip will be brought into contact with the sample through the hole in the intermediate plate. The feedback on this second tip will be accomplished by the tip scanning plate (17.2). In this emulation one of the tips is a straight tip and the other is a cantilevered tip, but the design is capable of using two straight or two cantilevered tips or one of each connected to either one of the two tip scanning plates.

[0032] The above two or three plate ultrathin SPM design can be readily used for optical cryostats and for cryostats in general. Cryostats have limited space, and the present microscope design is ideal for SPM in a cryostat. In the specific case of the optical cryostat there is limited space between parallel optical windows (18.1) and (18.2) through which radiation has to enter and exit. The present SPM design is ideal to be inserted between the windows labeled (18.1) and (18.2) in either the two (18.3) or three plate design. In terms of the cooling methodology that could be used, it could be cold braids (18.4) to cool the sample or a cold finger, or a surrounding liquid or gas coolant. In the case of braids (18.4) or a cold finger, the tip is at room temperature and this is an advantage in a tip scanning mode since the scanning range is affected by temperature.

[0033] Even though the design of this reconfigurable multiplate microscope has been described in terms of specific designs, the inventions are very general and can be applied to many other designs. For example, as illustrated in FIG. 19, the invention permits a tip scanning plate (19.1) to function without a bottom plate but with a large sample scanning stage (19.2) that can be chosen as to need. The tip scanner can also be attached to the lens of a regular microscope to have on line the tip and the lens viewing the sample.

[0034] The designs of the present invention are also generally applicable, such as those with the liquid cell, the tuning-fork, the new beam deflection methodologies etc. Also, the design is ideal for working with any type of tip, including without limitation, straight tip, cantilevered tip, regular silicon cantilevers, including those made specially for near-field optical applications, and gold tipped cantilevers that are made specially for apertureless near-field microscopy and for solid immersion lenses that can sit on the top plate of a dual plate microscope with fine adjustment of the SIL relative to the lens of the microscope.

[0035] Simply stated there has been no microscope with such functions previously.

[0036] Applications of the devices and methods of the invention encompass all areas of scanned probe microscopy and in addition, the two plate design allows the system to be very effectively used for fiber alignment and for automatic component assembly of integrated optical elements. For these latter applications, the system could have added lasers of welding and attachment of components or other devices for assembly.

[0037] Although the invention has been described in terms of preferred embodiments, it will be understood that numerous modifications may be made without departing from the true spirit and scope thereof, as set forth in the following claims. 

1. A device that is a two support scanned probe microscope including a top support plate and a bottom support plate, one support allowing for tip scanning and the other allowing for sample scanning, with an axis of the scanned probe microscope being free for incorporation into a beam directing system that requires the axis of the scanned probe microscope system to be free either from the top, the bottom, or both.
 2. A device as in claim 1, in which the top support can be hinged onto the bottom support and a rough approach is produced by a dc motor or other means and wherein said two supports are relatively movable with a large z range.
 3. A device as in claim 1, in which the top support is placed on the bottom support and a rough approach is produced by a dc motor or other means having the ability to produce a large z range. 4-66 (cancelled)
 67. A scanning probe device comprising: at least one support; means for mounting a sample at a sample location; a probe mounted on said support; and an aperture in said support aligned with said sample to provide a free optical axis; and at least one of said support and said sample location being scannable.
 68. The device of claim 67, wherein said aperture and said sample location are incorporated in a beam directing system.
 69. The device of claim 67, wherein said at least one support includes a first support and a second support spaced from said first support, and wherein said sample location is on said second support.
 70. The device of claim 69, further including an aperture in each of said supports, both apertures being aligned with said axis so that a beam from a beam directing system has a free channel to said sample location.
 71. The device of claim 70, wherein said first and second supports are relatively movable to position said probe with respect to said sample location.
 72. The device of claim 70, wherein said first and second supports are relatively movable in x-y planes, and where at least one of said supports is movable in a z direction perpendicular to one of said x-y planes to adjust the location of said probe with respect to said sample location.
 73. The device of claim 70, further including: an intermediate support located between said first and second supports; a second probe mounted on said intermediate support; and an aperture in said intermediate support aligned with said axis.
 74. The device of claim 70, wherein said means for mounting a sample is located in said aperture in said second support.
 75. The device of claim 67, further including a sensor for detecting the motion of said probe with respect to said sample.
 76. The device of claim 75, further including a feedback mechanism operable in response to the detected motion to adjust the location of said probe with respect to said sample.
 77. The device of claim 76, wherein said feedback mechanism includes a tuning fork adjacent said sensor.
 78. The device of claim 76, wherein said feedback mechanism includes an optical fiber detector adjacent said sensor for delivery of radiation to and collection of radiation from said sensor.
 79. The device of claim 67, further including a cryostat enclosing said at least one support while maintaining said free optical axis.
 80. The device of claim 67, further including a liquid cell at said sample location for containing a sample, said liquid cell being aligned with said optical axis for unobstructed viewing of said sample.
 81. The device of claim 67, wherein said probe is selected from the group of probes consisting of solid immersion lenses, silicon based apertured or nonapertured probes, and light concentrating nanoparticle probe tips.
 82. A scanning probe device comprising: first, second and third spaced apart and generally parallel supports relatively movable in corresponding x-y planes, means for mounting a sample at a sample location on a first one of said supports; first and second probes mounted on corresponding second and third supports; an aperture in each of said supports aligned with said sample to provide a free optical axis through said supports so that a beam from a beam directing system has a free channel to said sample location; and wherein at least one of said supports is movable in a z direction perpendicular to the x-y plane of the support containing said sample location to adjust the location of its corresponding probe with respect to said sample location.
 83. The device of claim 82, further including a feedback system for detecting and adjusting the locations of said sensors with respect to a sample at said sample location.
 84. The device of claim 83, wherein said optical axis is aligned with a beam directing system for a scanned probe microscope.
 85. A method for scanned probe microscopy, comprising: mounting a probe on a first scannable support; moving said support in x-y directions to scan said probe with respect to a sample; providing in said support an aperture having an axis aligned with said sample; illuminating said sample through said aperture by a beam directing system; producing a shadow or a point reflection on said sample; sensing properties of said sample when the sample is illuminated and when it is shadowed or has a point reflection; and detecting the differences between said sensed properties to produce an image of said sample.
 86. The method of claim 85, further including: producing said shadow or point reflection with said probe; moving said probe to obtain sensed properties of said sample; and repetitively detecting said differences to form said images.
 87. A method for scanned probe microscopy, comprising: mounting a probe on a first scannable support; scanning said support with respect to a sample; providing in said support an aperture having an axis aligned with said sample; and incorporating said support and probe in a beam directing system aligned with said axis.
 88. The method of claim 87, further including mounting the sample on a second support, and scanning said second support.
 89. The method of claim 88, further including adjusting the spacing between said first and second supports.
 90. The method of claim 89, further including mounting said probe on a resonator affixed to said first support.
 91. The method of claim 90, further including sensing the interaction of said probe and said sample.
 92. The method of claim 87, farther including cooling said sample and scannable support.
 93. The method of claim 87, further including illuminating said sample with an optical, electron optical, ion, atomic or molecular beam.
 94. The method of claim 87, wherein incorporating said support and probe in a beam directing system includes aligning a confocal optical microscope or an evanescent wave optical microscope with said axis.
 95. The method of claim 87, wherein scanning said support includes moving the support in x and y directions with respect to said sample location, the method further including: moving said sensor in a z direction with respect to said sample location; and sensing properties of a sample at said sample location as a function of the motion of said sensor in said z direction.
 96. A method for scanned probe microscopy, comprising: mounting a first probe on a first support; mounting a second probe on a second support; providing a sample location on a third support; providing in each said support an aperture having an axis aligned with said sample location to provide a clear optical channel to a sample at said sample location; scanning at least one of said supports to provide relative motion between at least one of said probes and said sample location; and incorporating said supports in a beam directing system. 